1. Field of the Invention
The present invention relates to a CCD (Charge Coupled Device) image sensor including PN junction photosensor elements and, more particularly, to a novel drive system for ensuring electrical isolation between the PN junction photosensor elements.
2. Description of the Prior Art
Recently, solid state image sensors have been developed for use in color video cameras. Solid state image sensors can be classified into an XY address image sensor type and a CCD image sensor type. The CCD image sensor has an advantage in an improved S/N ratio (signal to noise ratio) because the output capacity of the CCD image sensor is substantially small. In particular, an interline transfer CCD image sensor including PN junction photodiodes shows a high sensitivity to blue light, and exhibits a high resolution in combination with a mosaic color filter.
Normally, the CCD has a simple structure. However, various requirements in the function and the characteristics thereof made the structure of such a CCD somewhat complicated. The complicated structure requires increased number of masks and, therefore, the characteristics of the CCD image sensor have become variable.
In order to simplify the structure of the CCD image sensor including photodiodes, the present inventor has developed a novel structure, wherein channel stoppers are not required to electrically isolate photodiodes. An example of this structure is disclosed in copending application Ser. No. 515,038, "STRUCTURE AND DRIVING METHOD OF INTERLINE TRANSFER CCD IMAGE SENSOR", filed on July 18, 1983, by Shigehiro MIYATAKE, and assigned to the same assignee as the present application. The European counterpart is European Patent Application No. 83304183.3, which was published on Feb. 8, 1984 as No. 0 100 199 A2. Since the channel stoppers are not required between the photodiodes, the mask alignment operation is simplified. Thus, the characteristics of the CCD image sensor become constant.
However, the drive method disclosed in the above-mentioned application is of the frame storage type. Therefore, there is a possibility that a residual image is formed when objects move fast.